Plenty of posses Friends make Detroit their after-hours playground

You’ll find 400 or more people kicking a soccer ball around an athletic field on Belle Isle. Others scarf down pizzas in Eastern Market. A retro group twirls hula hoops in an art gallery.

What’s the group identity about? Authors Watts Wacker and Jim Taylor of the best-selling book 500 Year Delta suggest that the swarms of friends who frequent city hot spots are akin to a cohabitating affinity group. In other words, a posse.

These groups, which often encourage the intermingling of people regardless of age, race, gender or martial status, have erupted with the help of close-knit community supporters and the proliferation of social media.

Facebook, Foursquare, Twitter and the like allow people to decide spontaneously to join up with friends. (Or let them plan ahead to convene a fraternity of strangers.)

Said Todd Ridley, an Indian Village homeowner and self-styled city ambassador: “You come here and I’ll show you around. Everybody you know is one person away from knowing someone else.”